[SR-16026] Add external media support for DocC tutorial

[Kyle-Ye]

Previous ID	SR-16026
Radar	None
Original Reporter	@Kyle-Ye
Type	New Feature
Status	In Progress
Resolution

Additional Detail from JIRA

Votes	0
Component/s	Swift-DocC
Labels	New Feature
Assignee	@Kyle-Ye
Priority	Medium

md5: f30aa305e4b0b29fe297814fcf96541a

Issue Description:

Forums discussion here: https://forums.swift.org/t/can-we-link-and-render-external-images-that-is-from-urls/55098/6

Related issue: https://bugs.swift.org/browse/SR-15839

[d-ronnqvist]

This issue has a merged PR here #82 and should be considered resolved

[Kyle-Ye]

This issue has a merged PR here #82 and should be considered resolved

The #82 solves #185. And this issue is a follow-up to track the unfinished feature support for external media in tutorials.